The
fall line marks the geologic boundary of hard metamorphosed terrain—the product of the
Taconic orogeny—and the sandy, relatively flat outwash plain of the upper continental shelf, formed of unconsolidated
Cretaceous and
Cenozoicsediments. Examples of the Fall Zone include the Potomac River's Little Falls and the rapids in
Richmond, Virginia, where the
James River falls across a series of rapids down to its own tidal estuary.

Before navigation improvements such as locks, the fall line was generally the
head of navigation on rivers due to their rapids or waterfalls, and the necessary
portage around them. The
Little Falls of the
Potomac River is one example. Because of the commercial traffic, required labor and availability of water power to operate mills, numerous cities were founded at the intersection of rivers and the fall line.
U.S. Route 1 links many of the fall line cities.

In 1808,
Treasury SecretaryAlbert Gallatin noted the significance of the fall line as an obstacle to improved national communication and commerce between the Atlantic seaboard and the western river systems:[3]

The most prominent, though not perhaps the most insuperable obstacle in the navigation of the Atlantic rivers, consists in their lower falls, which are ascribed to a presumed continuous granite ridge, rising about one hundred and thirty feet above tide water. That ridge from New York to James River inclusively arrests the ascent of the tide; the falls of every river within that space being precisely at the head of the tide; pursuing thence southwardly a direction nearly parallel to the mountains, it recedes from the sea, leaving in each southern river an extent of good navigation between the tide and the falls. Other falls of less magnitude are found at the gaps of the Blue Ridge, through which the rivers have forced their passage...

Notable cities

Some cities that lie along the Piedmont–Coastal Plain fall line include the following (from north to south):

References

^"The Fall Line". A Tapestry of Time and Terrain: The Union of Two Maps - Geology and Topography. USGS.gov. Archived from
the original on 2011-05-14. Retrieved 2010-08-12. An alternate source claims the southern endpoint is farther west because there are "waterfalls & rapids":

^"History/Culture". PatapscoHeritageGreenway.org. Archived from
the original on 2010-03-10. Retrieved 2010-09-07. George Ellicott House: A block away is the 1789 George Ellicott House at 24 Frederick Road., which has been saved, moved out of the flood plain, and restored. The Ellicott family settled here along the fall line of the Patapsco River in 1772 and built an innovative, water-powered flour mill